Embodiments of the invention relate generally to electric drive systems including hybrid and electric vehicles and, more particularly, to rapidly charging energy storage devices of an electric vehicle using a multiport energy management system.
Hybrid electric vehicles may combine an internal combustion engine and an electric motor powered by an energy storage device, such as a traction battery, to propel the vehicle. Such a combination may increase overall fuel efficiency by enabling the combustion engine and the electric motor to each operate in respective ranges of increased efficiency. Electric motors, for example, may be efficient at accelerating from a standing start, while internal combustion engines (ICEs) may be efficient during sustained periods of constant engine operation, such as in highway driving. Having an electric motor to boost initial acceleration allows combustion engines in hybrid vehicles to be smaller and more fuel efficient.
Purely electric vehicles use stored electrical energy to power an electric motor, which propels the vehicle and may also operate auxiliary drives. Purely electric vehicles may use one or more sources of stored electrical energy. For example, a first source of stored electrical energy may be used to provide longer-lasting energy (such as a low-voltage “energy” battery) while a second source of stored electrical energy may be used to provide higher-power energy for, for example, acceleration (such as a high-voltage “power” battery or an ultracapacitor).
Plug-in electric vehicles, whether of the hybrid electric type or of the purely electric type, are configured to use electrical energy from an external source to recharge the energy storage devices. Such vehicles may include on-road and off-road vehicles, golf carts, neighborhood electric vehicles, forklifts, and utility trucks as examples. These vehicles may use either off-board stationary battery chargers, on-board battery chargers, or a combination of off-board stationary battery chargers and on-board battery chargers to transfer electrical energy from a utility grid or renewable energy source to the vehicle's on-board traction battery. Plug-in vehicles may include circuitry and connections to facilitate the recharging of the traction battery from the utility grid or other external source, for example.
Battery chargers are important components in the development of electric vehicles (EVs). Historically, two types of chargers for EV application are known. One is a standalone type where functionality and style can be compared to a gas station to perform rapid charging. The other is an on-board type, which may be used for slower C-rate charging from a conventional household outlet. EVs typically include energy storage devices such as low voltage batteries (for range and cruising, for example), high voltage batteries (for boost and acceleration, for example), and ultracapacitors (for boost and acceleration, for example), to name a few. And, in recent years, there has been much advancement in developing batteries having less weight, more energy storage capability, and less cost, as examples, resulting in many types of devices that may require re-charging in an EV application.
The effect of having many devices is generally compounded when considering that in some applications it is desirable to rapidly charge the storage devices using a “gas station” type charging system, while in other applications it is desirable to slow-charge the storage device using a conventional household outlet.
Thus, onboard charging devices have been developed that are configurable in order to accommodate charging multiple types of energy storage devices of electrical vehicles. Typically, such charging devices may include multiple ports that are connectable to one or more power sources, and also connectable via the ports to the various types of energy storage devices of an EV. Further, charging scenarios may vary from one occasion to another, leading to a desire to accommodate numerous charging scenarios as well as being able to accommodate multiple types of energy storage devices. For instance, in one charging situation an energy battery may be nearly fully depleted and other devices may not be depleted at all, while in another charging situation it may be desirable to “top off” the energy battery as well as one or more power devices. In either scenario, again as examples, only one high voltage may be available to provide the recharge energy, or a high voltage and a low voltage source may be dually available for more rapid charging. Thus, onboard charging devices are designed in order to manage a number of charging arrangements and devices connected thereto.
Conventional energy batteries in an EV application are typically not capable of accepting high C-rate charging current, such as at a rate that is known in the industry as a Level 4 charging rate. Thus, recent battery development has also been in providing a more rapid recharge capability in order to reduce charge time. As known in the art, rates of charging are typically dependent on and limited by the battery technology. However, as battery technology has improved, so has the ability to more rapidly recharge them as well. Thus, in some instances the battery itself is no longer the limiting factor in determining how rapidly it may be recharged and instead the charger itself may be the limiting device.
In other instances, the charger itself is not a functional limiter in determining how rapid a battery may be recharged. That is, the charger may be adequately designed in order to accommodate a Level 4 charging rate, as well. However, despite a capability to re-charge an energy storage device at a Level 4 charging rate, the charger may instead have a shortened life because of an increased temperature of operation during high-current recharge and because of ripple current that occurs during recharging. In system operation, current ripple typically occurs as contactors open and close and as the system transiently responds to contactor operation. Thus, life of the contactors and other charger components may be compromised because the higher current operation of Level 4 charging can exacerbate life degradation. In other words, although current ripple typically does occur in lower charging rate situations, because the overall current is lower than in a Level 4 arrangement, the ripple is typically not of enough magnitude to noticeably impact life of the charger and cause the charger to be an overall life limiter in a HV application.
Thus, when operating a charger in a Level 4 charging rate, life of components of the charger may be compromised based not only on an increased operating temperature, but also because the effect of current ripple is compounded with an increased current, as well.
It would therefore be desirable to provide an apparatus and method of increasing robustness in an energy charging device for an EV.